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package org.jbox2d.collision;

import org.jbox2d.common.Settings;
import org.jbox2d.common.Vec2;

/** A manifold for two touching convex shapes. Box2D supports multiple types of contact:
 * <ul>
 * <li>clip point versus plane with radius</li>
 * <li>point versus point with radius (circles)</li>
 * </ul>
 * The local point usage depends on the manifold type:
 * <ul>
 * <li>e_circles: the local center of circleA</li>
 * <li>e_faceA: the center of faceA</li>
 * <li>e_faceB: the center of faceB</li>
 * </ul>
 * Similarly the local normal usage:
 * <ul>
 * <li>e_circles: not used</li>
 * <li>e_faceA: the normal on polygonA</li>
 * <li>e_faceB: the normal on polygonB</li>
 * </ul>
 * We store contacts in this way so that position correction can account for movement, which is critical for continuous physics.
 * All contact scenarios must be expressed in one of these types. This structure is stored across time steps, so we keep it
 * small. */
public class Manifold {

	public static enum ManifoldType {
		CIRCLES, FACE_A, FACE_B
	}

	/** The points of contact. */
	public final ManifoldPoint[] points;

	/** not use for Type::e_points */
	public final Vec2 localNormal;

	/** usage depends on manifold type */
	public final Vec2 localPoint;

	public ManifoldType type;

	/** The number of manifold points. */
	public int pointCount;

	/** creates a manifold with 0 points, with it's points array full of instantiated ManifoldPoints. */
	public Manifold () {
		points = new ManifoldPoint[Settings.maxManifoldPoints];
		for (int i = 0; i < Settings.maxManifoldPoints; i++) {
			points[i] = new ManifoldPoint();
		}
		localNormal = new Vec2();
		localPoint = new Vec2();
		pointCount = 0;
	}

	/** Creates this manifold as a copy of the other
	 * 
	 * @param other */
	public Manifold (Manifold other) {
		points = new ManifoldPoint[Settings.maxManifoldPoints];
		localNormal = other.localNormal.clone();
		localPoint = other.localPoint.clone();
		pointCount = other.pointCount;
		type = other.type;
		// djm: this is correct now
		for (int i = 0; i < Settings.maxManifoldPoints; i++) {
			points[i] = new ManifoldPoint(other.points[i]);
		}
	}

	/** copies this manifold from the given one
	 * 
	 * @param cp manifold to copy from */
	public void set (Manifold cp) {
		for (int i = 0; i < cp.pointCount; i++) {
			points[i].set(cp.points[i]);
		}

		type = cp.type;
		localNormal.set(cp.localNormal);
		localPoint.set(cp.localPoint);
		pointCount = cp.pointCount;
	}
}
